Communications System Utilizing Orthogonal Linear Frequency Modulated Waveforms

1. A transmitter for transmitting a signal over a communications medium to a receiver, comprising: a data modulator for outputting a series of orthogonal sub-carriers carrying coded data; a linear frequency modulator for applying linear frequency modulation to said series of orthogonal sub-carriers to produce a series of sub-sweeps having orthogonal waveforms; and a multiplexor for producing a multiplexed output signal containing said series of sub-sweeps for transmission over said communications medium.

2. A transmitter as claimed in claim 1 , wherein said multiplexor comprises an inverse Fourier transform block for converting between frequency and time domain.

3. A transmitter as claimed in claim 1 , further comprising a control unit responsive to a performance metric characterizing the performance of said communications medium to adjust a bit rate assigned to said series of sub-sweeps.

4. A transmitter as claimed in claim 3 , wherein said performance metric is the average signal-to-noise ratio for said sub-sweeps.

5. A transmitter as claimed in claim 3 , wherein said control unit is configured to receive a response from the receiver containing an indication of the performance metric in response to a request from the transmitter.

6. A transmitter as claimed in claim 1 , wherein said data modulator is a data mapper for outputting grey-coded constellation data.

7. A receiver for receiving a signal over a communications medium from a transmitter, wherein the received signal contains a series of orthogonal sub-sweeps derived from a series of orthogonal sub-carriers carrying coded data, comprising: a demultiplexor for demultiplexing the received signal into said series of sub-sweeps; a linear frequency demodulator demodulating the series of sub-sweeps to produce the series of sub-carriers carrying the coded data; and a data demodulator for demodulating the series of orthogonal sub-carriers produced by the linear frequency demodulator to output a data stream.

8. A receiver as claimed in claim 7 , wherein the demultiplexor comprises a Fourier transform block for converting between frequency and time domain.

9. A receiver as claimed in claim 7 , further comprising a control unit configured to receive a training signal from the transmitter to measure a performance metric characterizing said communications medium, and to send a response message back to the transmitter to permit the transmitter to adjust a bit rate assigned to said series of sub-sweeps.

10. A receiver as claimed in claim 9 , wherein said performance metric is the average signal-to-noise ratio for said sub-sweeps.

11. In a communications system comprising a OFDM transmitter and receiver communicating data on a series of multiplexed sub-carriers, wherein the improvement comprises a linear frequency modulator is provided at the transmitter to subject the sub-carriers to linear frequency modulation to produce a series of sub-sweeps and a linear frequency demodulator is provided at the receiver to produce said sub-carriers from the received sub-sweeps.

12. A communications system as claimed in claim 11 , wherein the receiver is configured to measure a global performance metric for the communications medium and send a message to the transmitter containing an indication of said global performance metric to permit the transmitter to adjust a bit rate assigned to said series of sub-sweeps.

13. A communications system as claimed in claim 12 , further comprising a control unit responsive to said indication of said global performance metric to adjust said bit rate assigned to said series of sub-sweeps.

14. A method of establishing communication over a communications medium, comprising: creating a series of orthogonal sub-carriers carrying coded data; linear frequency modulating the sub-carriers to create a series of orthogonal sub-sweeps; and transmitting the series of orthogonal sub-sweeps as a multiplexed signal.

15. A method as claimed in claim 14 , wherein the sub-sweeps are multiplexed by applying an inverse Fourier transform.

16. A method as claimed in claim 15 , wherein the linear frequency modulation is applied in the frequency domain.

17. A method as claimed in claim 15 , wherein the linear frequency modulation is applied in the time domain.

18. A method as claimed in claim 14 , further comprising sending a request message for a performance metric indication to the receiver, receiving a response message from the receiver containing said performance metric indication, and adjusting a bit rate assigned to said series of sub-sweeps in response to said response message.

19. A method as claimed in claim 18 , wherein said performance metric indication is the average signal-to-noise ratio of said sub-sweeps.

20. In a communications system comprising a transmitter and receiver communicating data on a single sub-carrier, wherein the improvement comprises a linear frequency modulator provided at the transmitter to subject the sub-carrier to linear frequency modulation to produce a sub-sweep and a linear frequency demodulator provided at the receiver to produce said sub-carrier from the received sub-sweep.

21. A transmitter for transmitting a signal over a communications medium to a receiver, comprising: a data modulator for outputting a series of orthogonal sub-carriers carrying coded data; a multiplexer for producing a multiplexed signal containing said series of orthogonal sub-carriers; and a linear frequency modulator for applying linear frequency modulation to said multiplexed signal containing said series of orthogonal sub-carriers to produce a series of sub-sweeps having orthogonal waveforms for transmission over the communications medium.

22. A transmitter as claimed in claim 21 , wherein said multiplexer is an inverse Fourier transform block.

23. A receiver for receiving a signal over a communications medium from a transmitter, wherein the received signal contains a multiplexed series of orthogonal sub-sweeps derived from a series of orthogonal sub-carriers carrying coded data, comprising: a linear frequency demodulator demodulating the multiplexed series of sub-sweeps in the received signal to produce an output signal containing the sub-carriers; a demultiplexor for demultiplexing the output signal of the linear frequency modulator to produce the series of orthogonal sub-carriers; and a data demodulator for demodulating the series of orthogonal sub-carriers produced by the demultiplexor to output the coded data.

24. A receiver as claimed in claim 23 , wherein the demultiplexer is a Fourier transform block.